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If a new report is to be believed, an entire generation of children has grown up drinking a toxic chemical from their earliest months: bisphenol A. A consortium of North American environmental and health groups released a paper Thursday showing that many major-brand baby bottles leach bisphenol A, and is now calling for a moratorium on the use of the compound  used to make polycarbonate plastic  in food and beverage containers.

Researchers tested 19 baby bottles purchased in nine U.S. states and Canada. Bottle brands included Avent, Dr. Brown, Evenflo, Disney, Gerber and Playtex. When the bottles were heated to 175 degrees F (80 degrees C), every one of them leached bisphenol A at about 5 to 7 parts per billion. The report also suggested that because of the chemical makeup of bisphenol A, it may leach more in fatty or acidic liquids, such as milk or apple juice, than in water.

It's a parent's nightmare. But before you panic, consider this: U.S. and E.U. health and environment authorities still stand behind polycarbonate plastic, putting the safe level of daily bisphenol A exposure at more than 25 times the levels found in baby bottles. (The Canadian agency, Health Canada, is currently reviewing its bisphenol A policy; conclusions are due in May.)

So who's right? Opponents of bisphenol A say official safety figures are far too high, given what the chemical, which mimics the hormone estrogen in the body, does in animals. In the lab, even low exposure levels  adjusted for body weight  have been linked to a variety of sex-hormone-imbalance effects, including breast and prostate cancer, early puberty, miscarriage, low sperm count, and immune-system changes. Critics also claim that in developing infants, such sex-hormone effects may come into play at exposure levels far below what health authorities have deemed safe for adults. "The reproductive system is developing, the brain is developing, the immune system is developing," David Carpenter, director of the Institute for Health and the Environment at the University at Albany, told a news conference Thursday on behalf of the environmental agencies. Knowing that, he said, it is "absolutely obscene" to expose infants to the compound. Legislation has been proposed in several U.S. states to limit or ban the use bisphenol A. And a handful of stores, including Whole Foods and Patagonia, have yanked polycarbonate bottles from their shelves.

Still, the scientific establishment disagrees. In a 2006 summary explaining its review of bisphenol A safety, the European Food Safety Authority argued that animal trials of the chemical simply don't tell us very much about humans. For one thing, when humans ingest the compound, it's quickly excreted through the urine; when rats and mice eat it, it's released into the bloodstream and remains in the body much longer  with much more time to throw off the body's sex-hormone balance, causing nasty effects.

So far, the human data on bisphenol A have been "really inconclusive," says Antonia Calafat, a research chemist at the Centers for Disease Control and Prevention, citing a lack of big quality studies testing the chemical's effects in humans. In order to prove definitively that bisphenol A is not harmful to people, researchers would need to conduct large, lengthy trials, such as those that finally concluded that thimerosal-containing vaccines do not cause autism in children. That would require rounding up a control group of participants with very little exposure to bisphenol A  no small feat. Calafat's recent findings showed that, among roughly 2,500 Americans tested in 2003 and 2004, more than 95% already had traces of bisphenol A in their urine. Alternatively, researchers could test how higher-than-average doses of bisphenol A affects people. Again, a likely dead end. "As a scientist it would be pretty much unethical to do that study knowing what [bisphenol A] does in animal studies," says Laura Vandenberg, a post-doc fellow at Harvard Medical School who researches bisphenol A, and is a critic of its use.

The obvious solution may seem to be, when in doubt, ban it. If there's a chance that bisphenol A hurts kids, then why run the risk? Certainly, parents have little interest in waiting for scientific evidence when they think their children's health is in danger. Hence, the many state legislators who want to limit bisphenol A's use now. But without evidence, anything could be considered potentially harmful. Right now, U.S. and E.U. health and environment authorities still believe the best evidence supports continued use of regular polycarbonate baby bottles.

Polycarbonate plastic is used for a reason: It's useful. Hard, shatterproof, lightweight and clear, it's in a huge range of products from water bottles and food storage containers, to lenses in eyeglasses and car headlights, CDs and DVDs, and even bulletproof glass. "Whether you realize it or not, you use it in your life every day," says Steven Hentges, head of the polycarbonate group at the industry lobby organization American Chemistry Council. There are, of course, alternatives to polycarbonates, like glass and other plastics. And for the growing number of consumers opposed to bisphenol A, there's no shortage of online resources to help find them.